Higher alkyl thiurom sulfide

ABSTRACT

Blends of EPDM with highly unsaturated rubbers are co-cured with sulfur using as accelerators higher alkyl thiuram disulfides (e.g., tetralaurylthiuram disulfide) or benzothiazylsulfenamides (e.g., N-lauryl-benzothiazylsulfenamide).

States Patent 1 llsamala el al.

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HIGHER ALKYL THIUROM SULFIDE Inventors: Teruyoshi Usamoto, Osaka;

Yasutaka I-latada, Higashi-Osaka; Itsuro Furuichi, Yoyonaka City; MasaoMatsuo, Takatsuki, all of Japan Assignee: SumitomaChemical Company,

US. Cl. 260/567, 260/4 R, 260/23.7 M,

260/415 R, 260/795 B, 260/429 K, 260/889 Int. (11... C0711: 155/10 Fieldof Search 260/567 References Cited UNITED STATES PATENTS 4/1972 Hudginset a1 260/567 X FOREIGN PATENTS OR APPLICATIONS 4,215,783 8/1967 JapanOTHER PUBLICATIONS Fischer e1; a1., Industrial and EngineeringChemistry, Vol. 51, N0. 2, pp. 205-208, (Feb. 1959).

Primary ExaminerLeon Zitver Assistant Examiner-Michael W. GlynnAttorney, Agent, or Firm.lames J. Long 5 7] ABSTRACT Blends of EPDM withhighly unsaturated rubbers are co-cured with sulfur using asaccelerators higher alkyl thiuram disulfides (e.g., tetralaurylthiuramdisulfide) or benzothiazylsulfenamides (e.g., N-laurylbenzothiazylsulfenamide).

1 Claim, N0 Drawings HTGHIER ALKYL THIUROM SULFllDE This application isa continuation-impart of our copending application Ser. No. 70,934,filed Sept. 9, 1970, now U.S. Pat. No. 3,706,819.

This invention relates to a co-vulcanizable composition comprising ablend of EPDM rubber and ahighly unsaturated rubber. Moreparticularly,the invention relates to such a co-vulcanizable blend of rubberscontaining, as the accelerator, a compound which displays only a rathersmall difference in solubility in each of the rubbers.

Certain defects of highly unsaturated rubbers (such as natural rubber,styrene-butadiene rubber and polybutadiene rubber) such as a lack ofozone-resistance, weather-resistance and heat resistance can becompensated for by adding EPDM rubber, which has excellent properties inthose respects. Unfortunately, the mechanical strength of the rubberblend, upon vulcanization, does not reach the arithmetic mean of themechanical strengths of the component rubbers. This is a seriousshortcoming in practical. applications, The fact that the mechanicalstrength reaches the minimum when the ratio of EPDM and highlyunsaturated rubber is in the neighborhood of 75/25 means that as apractical matter only small amount of EPDM may be mixed, thereby makingit very difficult for example to improve the tackiness, adhesion andworkability of EPDM by adding a small amount of a highly unsaturatedrubber to EPDM. Therefore, it is an urgent task to provice mixtures ofEPDM rubber and a highly unsaturated rubber such that mechanicalstrength of the mixture may be proportional to the arithmetic mean ofthe mechanical strengths of the component rubbers of mixture, at allmixing ratios.

' The present inventors have studied in detail each factor which governsthe co-vulcanization of the mixtures of EPDM and a highly unsaturatedrubber in order to solve this problem. As a result, we'attained newknowledge and developed the techniques of this invention which enablesthe co-vulcanization of the mixtures to be easily achieved.

though the difference of the vulcanization velocities With mixtures ofEPDM and a highly unsaturated I rubber compounded for sulfurvulcanization, the difficulty in attaining co-vulcanization of themixtures has been explained as arising mainly from the considerabledifference in the vulcanization velocities of EPDM and a highlyunsaturated rubber. That is, as the vulcanization velocity of the formeris extremely slow, compared with that of the latter, the vulcanizationis not uniform between the different rubber phases of the vulcanizedrubber mixture of EPDM and a highly unsaturated rubber, and thecross-linking between the different rubber phases is not sufficient,thereby reducingthe rupture strength of the vulcanized rubber mixture toa great extent.

Actually, with a mixture of EPDM and styrenebutadiene rubber, use oforganic peroxides for vulcanizing agents leads to a vulcanized rubberwhose mechanical strength may be proportional to the arithmetic mean ofthose of the component rubbers of the mixture, and even if thevulcanizing agents are sulfur compounds, an increase of the degree ofunsaturation of the EPDM to be mixed with the'styrene-butadiene rubberresults in improvement of the mechanical strength.

Therefore, we 'may considerit an extremely important, necessarycondition to increase considerably the vulcamay be extremely large withthe: latter, depending on the combination of rubbers to be mixed. Thisfact indicates that there exist important factors which govern theco-vulcanization of EPDM rubber blends, in addition to the difference inthe vulcanization velocities of component rubbers.

The inventors have systematically measured the solubilities of variousaccelerators, including commercially available vulcanizationaccelerators, in EPDM and various rubbers, and have studied therelationships between the solubility and the co-vulcanizability ofvarious EPDM mixtures to which the vulcanization accelerators used inthe measurement were added. As a result, we found, surprisingly, thatthere exists an interrelation between solubility and co-vulcanizability.Firstly, we found that a vulcanization accelerator exhibits considerablydifferent solubility in each rubber, and, therefore, the vulcanizationaccelerator is distributed in different concentration in each rubberphase of the mixture. Even if a vulcanization accelerator is blendedwith each rubber at the same concentration prior to blending therubbers, the vulcanization accelerator easily shifts around in the blenddue to diffusion of molecules, finally beingre-distributed in accordancewith the ratio of the solubili ties. Secondly, since: the difference inthe solubility varies greatly depending on the type of vulcanizationaccelerator, a vulcanization accelerator which has solubilitiesresembling more closely those of EPDM and a highly unsaturated rubber tobe mixed with the former leads to a better co-vulcanization of themixture of the EPDM and the highly unsaturated rubber. Finally, we,found that the replacement of methyl, cyclohexyl groups, etc. oftetramethyl thiuram monosulfide and N-cyclohexyl benzothiazylsulfenamide by alkyl groups of higher numbers of carbon atoms brings thesolubilities of the vulcanization accelerators in EPDM and a highlyunsaturated rubber closer together, and that use of the saidvulcanization accelerators leads to a considerable improvement of theco-vulcanization of the mixtures of EPDM and a highly unsaturatedrubber.

According to the study of the present inventors, most of theconventional, commercially available vulcanization acceleratorsincluding those which slightly improve the co-vulcanizability, such asN-cyclohexyl benzothiazyl sulfenamide andN-oxydiethylene benzothiazylsulfenamide, exhibit solubilities in highly unsaturated rubbers severaltimes higher than in EPDM. Especially with vulcanization. acceleratorsof the thiuram and dithioate groups, the solubilities in highlyunsaturated rubbers become more than 10 times as large as those in EPDM,and those vulcanization accelerators are very easily dissolved in highlyunsaturated rubbers. ln additiomwe found that the co-vulcanizability ofa mixture of EPDM and a highly unsaturated rubber to whichavulcanization accelerator of the thiuram or dithionate group is addedis considerably inferior to that of the same rubberto which a.vulcanization accelerator of the sulfenamide group is added. Although N-cyclohexyl benzothiazyl sulfenamide and N- oxydiethylene benzothiazylsulfenamide are vulcanizahas the same solubility parameter as EPDM or ahighly unsaturated rubber. Methyl cyclohexane and carbon terachloridemay be used as equivalent solvents for EPDM and SBR respectively. Thevalue obtained by dividing the solubility in carbon tetrachloride bythat in methyl cyclohexane is called the solubility ratio.

The number of carbon atoms in the substituents of the vulcanizationaccelerators are very important for the following reasons. On the onehand, a larger number of carbon atoms in the alkyl groups leads to anincrease in the affinity for EPDM, consequently an increase in thesolubility. On the other hand, an increase of the number of carbon atomsresults in an increase of canization agents depends on the solubilitiesof a vulcanization accelerator (to be blended with the mixture) in theEPDM and the highly unsaturated rubber. That is, the most importantnecessary condition for co-vulcanizability is that the solubilities ofthe vulcanization accelerator in both rubbers should be as close aspossible to each other. Commercially available vulcanizationaccelerators, however, do not necessarily satisfy this necessarycondition. A group of vulcanization a ccelerators has been found by thepresent inventors which satisfy the necessary condition, and this groupshows' an amazing co-vulcanization effect when blended with a mixture ofEPDM and a highly unsaturated rubber.

The vulcanization accelerators to be used in the pres ent invention arechemicals having the general formula (I) or (2) or mixtures thereof. Themixingration may be appropriately chosen depending on the desiredproperties of a vulcanized rubber.

(where R,, R R and R are the same or different and are alkyl groupshaving together a total of at least 26, preferably 30, carbon atoms;preferably at least two of the Rs have 12 to 18 carbon atoms; in somecases all of the Rs have 12 to 18 carbon atoms; x represents an integerof l to 4).

are blended'witha mixture .of EPDM and a highly unsaturated rubber, theywill be uniformly dissolved or dispersed. The solubility here means thesaturation solubility of a vulcanization accelerator in a solvent whichthe molecular weight per radical and hence a larger amount of thechemical must be used, thereby increasing the cost.

On the other hand, if the number of carbon atoms is small, thesolubility ratio becomes large, leading to degradation of the propertiesof the vulcanized mixture. Therefore, the number of carbon atoms in thealkyl substituents of the vulcanization accelerators should preferablybe 12 to 18 for the accelerators having general formulae (1) and (2).

'The EPDMs which may be employed in this inven tion, are terpolymersconsisting of ethylene, propylene and non-conjugated diene. The range ofthe ethylene/- propylene ratio is 20/80 to /20, by weight, while thenon-conjugated diene content ranges from 2 to 20 percent by weight.Examples of the non-conjugated dienes are 1,4 -hexadiene,dicyclopentadiene, S-methylene-Z- norbornene, 5-ethylidene-2-norbornene,and 4,7,23,9- tetrahydroindene.

Examples of highly unsaturated rubbers which may be used in the presentinvention, are conventional, commercially available natural rubbers,polyisoprene, rubber, styrene-butadiene rubber, styrene-acrylonitrilerubber, polybutadiene rubber, polychloroprene rubber, etc. Those rubbersmay be used alone or in a combination for blending with EPDM. They areconjugated diolefin polymers, whether homopolymers or copolymers with upto 50 percent of a copolymerizable monoethylenically unsaturated monomer(e.g., styrene, acrylonitrile, vinyl pyridine, ethyl acrylate, methylmethacrylate, etc.). Mixtures to be used in this invention should havethe following compositions for effective results: EPDM, to 25weight-percent, and highly unsaturated mbber, 15 to 75 weight-percent.

Other than the accelerator, there is no special restriction oncompounding ingredients such as sulfur, auxiliary agents and reinforcingfillers. Plasticizers, fire retarding agents, pigments, etc. may be alsoblended, if desired.

Ordinary mixing rollers, and mixers may be employed for preparing therubber compositionsof this invention. The compositions may be mixed andblended by ordinary mixing methods and under ordinary mixing conditions.The co-vulcanized rubber products obtained from the rubber compositionsofthe present invention are useful in various fields such asautomobiles, vehicle parts, industrial parts, electric parts, andbuilding materials, because of their excellent mechanical properties aswell as their excellent ozone, weather, heat, and, chemical resistingproperties and excellent electrical properties. Especially, the rubbercompositions of the present invention will be very useful for developingthe application of co-vulcanized rubbers containing EPD M'of' more than40 weight percent.

White sidewalls or cover strips for pneumatic tires, made of thecomposition of the invention, are ozoneresistant and display goodadhesion to a tire carcass made of highly unsaturated rubber.

in the following we shall explain this invention referring to Examples,but it should not be considered that this invention is restricted tothose examples only.

EXAMPLE 1 Two kinds of mixtures as shown in the following table areprepared. Both mixtures are blended together at an arbitrary weightratio. Let us call the weight ratio (EPDM- mixture/8BR mixture) asblending ratio. The EPDM may be ethylene-propylene-S-ethylidene-2-norbornene terpolymer containing 43 percent propylene by weight, iodinenumber 20.

Blending Ratio Then, the blended rubbers are press-vulcanized for 30minutes at 150C. under a pressure of 50 Kglcm The tension test of thevulcanized products is carried out in accordance with JISK 6301:specimens of No. 3 dumbbell shape of 2 mm thick are stretched at astretching speed of 500 mm/min by means of a Shopper type tension testermanufactured by Shimazu Seisakusho Co., Ltd. The results are shown inthe following table together with the results for tetramethyl thiurammonosulfide (TS) which are a widely used thiuram group vu1- canizationaccelerator and those for tetrabutyl thiuram disulfide (TBT) which hasthe longest linear chain hydrocarbon radicals among the commerciallyavailable thiuram group vulcanization accelerators.

Tensile Strength (Kg/cmfl 100/0 75/25 50/50 /75 0/100 Accelerator:Solubility Ratio Tetralauryl Thiruam disulfide 2 196 165 168 177 202 TS(control) 57 190 35 76 122 166 TBT (control) 193 87 95 .140 185 Thetensile strength of the vulcanized rubber mix- EPDM ixt e 5BR Mixtur'3tures to which the vulcanization accelerator of improved solubility ismixed, is very large, clearly indicat- EPDM produced by us. ing theimprovement. Uniroyal 100 parts SBR produced by Nippon EXA PLE 2Synthetic Rubber Co. M JSR 1500 100 parts I HAF Black pans 50 pans Thefollowing types of EPDM s which contain a third Process 011 15 parts 15parts Component are used, and the same operations and test g w g P tParts are carried out. The following tables give the results.

ar o s w 15 52;, 5 g Blending and vulcanization of EPDM produced by0.0076 mole 0.0076 40 Vulcanization accelerator mole An EPDM mixture anda SBR mixture to which one US. Uniroyal (ethylene/propylene weight ratio/35, 5 percent by weight of dicyclopentadiene) and JSR 1500, SBRproduced by Nippon Synthetic Rubber (30., Ltd.

Tensile Strength (Kg/cm) Blending ratio 100/0 /25 50/50 25/75 0/100Solubility Accelerator: Ratio Accelerator used in this Example 2 196 97123 167 202 TS (control) 57 201 35 77 126 166 TBT (control) 210 45 88147 185 adds tetralauryl thiuram disulfide (a vulcanization accelera'torof thiuram group), having the following structural formula, areprepared. Both mixtures are blended with various weightratios.

Blending and vulcanization of Nordel 1040, EPDM produced by the US. duPont Co. (the third component is 1,4-hexadiene) and JSR 1500, SBRproduced by Nippon Synthetic Rubber Co., Ltd.

Tensile Strength (Kg/cm Blending ratio /0 75/25 50/50 25/75 0/100Solubility Accelerator: Ratio Accelerator used in this Example 2 191 131170 202 TS (control) 57 198 37 75 166 TBT (control) 195 56 90 EXAMPLE 3N-lauryl benzothiazyl sulfenamide having the following structuralformula is blended, followed by the same operations and test as inExample 1. The tensile strength of the mixtures after vulcanization isshown in the following table.

I oil extracted into hexane. The hexane was removed in vacuo to give60.6 g. of oil which solidified when 10 cooled. The solid wasrecrystallized from ethanol to obs tain 30 g. of colorless crystallineproduct mp 40-41C.

Tensile Strength (Kglcm Blending ratio 100/0 75/25 50/50 /75 0/100Solubility Accelerator: Ratio Accelerator Less than 195 184 186 190 210used in this 2 Example CZ(control) More than 198 123 124 175 228Comparison with N-cyclohexyl benzothiazyl sulfena- Anal Calcd. for C H NS C, 63.58; H, 10.60; N, mide (CZ) which is known to be very suitablefor vul- 4.63; S, 21.19. Found. C, 64.05; H, 10.80; N, 4.84; S,canization of a mixture shows that the vulcanization ac- 25 21.66.

celerator of this invention has a superior property.

The foregoing examples may be repeated, using such accelerators asN,N'-di-n-propyl-N,N'-ditetradecyl thiuram disulfide, tetrastearylthiuram monosulfide, N,N- diisopropyl-N,N-didodecyl thiuram mono-, ordisulfide, N,N-diisopropyl-N,N'-dioctadecyl thiruam di-N,N'-diisobutyl-N,N'dioctadecyl thiruam disulfide, tetralauryl thiurammono-, di-, tri-, or tetra-sulfide, tetrapentyl thiuram disulfide,N-methyl- N-dodecyl benzothiazyl sulfenamide, N-dodecyl benzothiazylsulfenar'nide, N-cyclohexyl-N-hexadecyl benzothiazyl sulfenamide,N-hexyl-N-octadecyl benzothiazyl sulfenamide, N-isopropyl-N-dodecylbenzothiazyl sulfenamide, etc. The accelerators of formulas (1) and (2)are new chemicals.

Examples of preparations of the chemicals are as follows:

N-dodecyl-N-isopropyl-2-benzothiazole sulfenamide. Chlorine (14.2g) wasadded to a suspension of 68g of benzothiazoyl disulfide in 500 ml ofethylene dichloride. Theresulting solution was added to a solution of90.8g. of N-isopropyl-N-dodecy-lamine and 40.4g of triethylamine in 450ml. of ethylene dichloride at 2025C. over a one hour period.The'reaction mixture was stirred for 15 minutes at which time the aminehydrochloride was removed by filtration. The solution was concentratedby removing solvent under vacuum and additional solid was removed byfiltration. The product was obtained as a brown oil by evaporating theremaining solvent. I

Anal. Calc. for 'Found N, 6.70; S, 16.26

N,N-'di-n-docecyl-N,N'-diisopropylthiuram disulfide.

solution of 8g. of sodium hydroxide in 150 ml. of water was added to asolution of 45.4 g of N-isopropyl- N-dodecylamine in 100 ml. of ethanol.To the stirred mixture was added dropwise 16 g of carbon disulfide.

EXAMPLE 4 A masterbatch is mixed in a Banbury containing (by weight) 50parts NBR (31 percent acrylonitrile), 50 parts EPDM (E/P ration 60/40;10 percent ethylidene norbornene), 50 parts carbon black, 5 parts zincoxide, and 0.75 part stearic acid. Three portions of the masterbatch(designated A, B and C) are mixed with 2.5 parts sulfur (phr) andapproximately equimolar quantities of accelerator as follows: (mm per grubber) tetramethyl thiuram disulfide tetraethyl thiuram Allthree stocksare cured for 10 minutes at 320F. The physical properties are asfollows:

A B C Tensile strength. pai 750 800 I 1680 Elongation at break, 230

dioctadecyl thiuram disulfide.

1. A CHEMICAL WHICH IS N,N''-DIISOPROPYL-N,N''-DIOCTADECYL THIURAMDISULFIDE.